Add dimension continuation creation policy

src/command.rs

@@ -1248,6 +1248,9 @@ pub enum CmdResult {
     CommitDimension {
         entity: EntityType,
         association: DimensionAssociationInput,
+        /// Retain the source dimension's layer and style instead of replacing
+        /// them with the current creation defaults (DIMCONTINUEMODE=1).
+        preserve_base_style: bool,
     },
     /// Commit a Model-tab 3D solid: the acadrust entity (for selection /
     /// persistence) plus its B-rep (cached for boolean ops + shaded